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99gst_racer

Brake light and ABS come on intermittently

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The lights both come on at the same time, and it happens about once every 2-4 weeks. Once I shut the engine off and turn it back on, they're gone. Things I know:

 

- Brake fluid is at the proper level

- The brake pedal has always been very spongy and crappy feeling

- ABS kicks in when it shouldn't (any little bump while braking)

 

 

Is there any common fail points in the brake system that could cause these issues? Like a sensor or a module? I figured I'd ask here before paying a dealership to diagnose it.

 

 

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Edited by PVolk

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Try a brake bleed?

 

I haven't yet only because I really hate bleeding brakes. I didn't want to do it unless I had to.

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Best bet would be to go ahead and get it scanned for codes before deciding a course of action. I only suggest the bleed when you stated a spongy feeling to your pedal. I can appreciate how much the job sucks because I've done it few time on vehicles..never goes easy for me.

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I assume dealerships have scanner tools that diagnose beyond a check engine light? Would they be able to diagnose it even if the lights were off?

 

I've never once taken a vehicle to a dealership for service, so this would be new territory to me.

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If your light has come on then there should be a code stored, so providing that you haven't had codes cleared then yes the dealership will be able to diagnose even without lights. This will save you replacing parts that may not be bad. I don't care for paying for diagnosing myself but most times it pays off to pay this fee once and replace proper parts than to "pay" for time spent on wrong parts being replaced.

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Looks like it is either a bad ground wire, speed sensor, or ECBM:

 

 

 

There are two very common issues with these models that can cause those two lights to illuminate:1) faulty Electronic Control Module (EBCM) and 2) faulty wheel sensors.

 

 

 



The EBCM will set specific codes indicating an internal malfunction. This is often cause by either a poor ground situation on the drivers side frame rail, just under the drivers door and also caused by a faulty EBCM. If the EBCM is indeed faulty, it can be rebuilt. I have sent many to www.modulemasters.com for repair. They are affordable and quick.

 

If you have wheel speed sensor codes, we would need to know if they are performance codes or "circuit" codes. Performance codes indicate that the sensor has checked out electronically, but fails to give a valid signal. For performance codes, the sensors usually need cleaned. The tip of the sensor slides into a hole on the wheel hub assembly and the base of the sensor bolts to the outside of the hub. Rust and corrosion can build up under the sensor and push the sensor tip away from what it reads, causing low signal output. Removing the sensor from the hub, allows you to clean rust and corrosion from the sensor mounting surface restoring the factory clearance. You DO have to take the rotor and caliper off to perform this.

 

A "circuit" code indicates that the sensor has failed electronically and requires replacement. The procedure is the same as cleaning the sensor, only instead of re-installing the old sensor, you install a new one.

 

For either wheel speed sensor case, you will want to check the free play of the wheel bearing. There should be NO free play in the bearing, although a very little is acceptable. Excessive free-play can cause codes as the inner part of the bearing moves to and away from the sensor mounted to the outside of the bearing (hub).

 

 

 

http://www.justanswe...termitenly.html

Edited by jBlaze3000

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Yeah, you could scrape the grounds clean and see if that improves the issue's, other than that, you will have to start swapping parts.

Edited by Carder09

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My wifes 2003 yukon xl did the same thing as yours. It ended up being the brake control module. a replacemjent part was about $700. i sent my off to module master and had it rebuilt for $150. it was easy to remove and comes with a 5 year warranty. The whole process took about a week.

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Is the vehicle out of commision while the module is off being rebuilt? Or can I continue to drive it while I wait?

 

 

EDIT: just answered my own question.

 

"You can still drive your vehicle since the brakes will not be impaired by removal of the ABS module. On certain vehicles, the speedometer receives an input signal from the ABS module and may not function until the module is back in place."

Edited by PVolk

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Check G110, near #1 body mount and G100 which is battery negative cable to frame , make sure it is mounted to the frame and not the core support. For ABS activating , remove the front wss's and clean the mounting usrface with die grinder and sanding disc. Did you ever have the codes checked?

Edited by debo511

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Is the vehicle out of commision while the module is off being rebuilt? Or can I continue to drive it while I wait?

 

 

EDIT: just answered my own question.

 

"You can still drive your vehicle since the brakes will not be impaired by removal of the ABS module. On certain vehicles, the speedometer receives an input signal from the ABS module and may not function until the module is back in place."

 

 

do not just take the ebcm to get rebuilt without the truck getting scanned and diagnosed !!!

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As Govtech stated, have it scanned first before you start thowing money at it. I cleaned all 3 of my VSS sensors, they were fine though. I also flushed the entire brake system and cleaned the grounds and still had the issue.

 

Sent mine to module masters and it works great now, also saved me $400 that the selling dealer took off of the price of the truck when I bought it.

 

Very easy to do, as long as you have one of the rebuildable modules. There are 3 of them if memory serves me right, only one can be fully rebuilt.

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Anybody have a pic of where the ground wire attachs to the chassis? I didn't see it when I checked yesterday.

 

The good news is that I have the KH325 module, so it is rebuildable if it comes down to it.

 

I'll take it in to get is diagnosed sometime soon.

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ground is under your left foot on rear side of body mount bracket

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